1. Field of the Invention
The invention relates to a face seal assembly. The invention relates in particular, but not exclusively, to a face seal assembly suitable for sealing the drive shaft of a charge compressor in an internal combustion engine relative to a compressor housing.
2. Description of the Related Art
Particular attention has to be paid in regard to the special operating conditions when sealing the drive shaft of e.g. an. turbine-driven centrifugal or screw compressor or a turbocompressor driven by an exhaust gas loaded turbine. For instance the drive shafts of such compressors generally have a very small diameter, e.g. less than 40 mm. These shafts rotate at very high speeds of e.g. 10.sup.5 min.sup.-1 and more. Further the seal may be subjected to pressures above as well as below atmospheric pressure conditions prevailing in the housings of such compressors. Moreover the gaseous medium to be sealed, which is generally air, must be kept free of non-gaseous constituents such as oil particles. Oil particles may be contained in a portion of the compressor located externally of the compressor housing for accomodating roller bearings or the like for supporting the shaft, relative to which portion the interior of the compressor has to be sealed. In view of the critical operating conditions, labyrinth seals have long been preferred for such applications although labyrinth seals have the inherent disadvantage of a relatively high leakage. A face seal assembly has not yet been take into consideration as alternative to labyrinth seals for such applications despite of the much lower leakage of face seals. It has been found that the seal rings of prior face seal assemblies because of a dry running became so hot that a premature break-down of the seal occurred. Similar results were obtained with prior face seal assemblies when these were subjected to negative pressure conditions and the operating speeds significantly reduced.
An object of the invention is to provide an improved face seal assembly. Another object of the invention is to provide a face seal assembly having minimum danger of dry running and a reduced leakage under operating pressures above as well as below atmospheric pressure conditions. Still another object of the invention is to provide a face seal assembly suitable for sealing the shafts of turbo compressors having a small diameter.